The present invention relates to a bendable tube of an endoscope, which bendable tube is constituted by linearly arranging a plurality of joint rings and pivotally connecting adjacent ones of them by means of shaft pins.
In an insertion section of an endoscope, a bendable tube is provided between a resilient tube and a distal portion. The bendable tube is forcibly bent by a pulling operation performed on the proximal-end side by means of manipulation wire elements. In an ordinary bendable tube, a plurality of joint rings are linearly arranged in the longitudinal direction of the insertion section of the endoscope and, with ear portions of adjacent joint rings overlapped, the overlapped ear portions are pivotally connected by means of shaft pins (see Jpn. U.M. Appln. KOKAI Publication No. 60-187702).
FIGS. 9 and 10 show the structure of a conventional bendable tube. As is shown in FIG. 9, a bendable tube 50 is constituted such that a plurality of joint rings 51 are linearly arranged in the longitudinal direction of an insertion section and, with mutually opposed ear portions 52 and 53 of adjacent joint rings 51 overlapped, rivet-like shaft pins 56 are passed through insertion holes 54 and 55 formed in the ear portions 52 and 53. One end of each shaft pin 56 is caulked on one of opposed ear portions, 52. Thus, adjacent joint rings 51 are pivotally connected.
Needless to say, the width of each ear portion 52, 53 should be as small as possible in order to reduce the diameter of the bendable tube 50 and to reduce as much as possible the distance of that portion of the pivotal connection section, which projects toward the center of the inner cavity of the bendable tube 50. However, since the insertion holes 54 and 55 for insertion of the shaft pins 56 need to be provided and the mechanical strength for caulking has to be maintained, it is necessary that the ear portions 52, 53 have certain widths.
In an example shown in FIG. 10, the width of the ear portion 52 located inside is made different from that of the ear portion 53 located outside in order to achieve reduction in diameter of the bendable tube 50 while maintaining maximum widths of the ear portions 52 and 53 and to reduce as much as possible the distance of projection of the ear portion 52, 53 toward the center of the inner cavity of the bendable tube 50. The width of the ear portion 53 located outside is made less than that of the ear portion 52 located inside, and the insertion holes 54 and 55 are modified stepwise accordingly.
In this case, however, when the joint rings are pivotally connected, the ear portions of the adjacent joint rings of the bendable tube are overlapped, the rivet-type shaft pin is passed through the insertion holes of the overlapped ear portions, and one end of the shaft pin is caulked on one of the overlapped ear portions. Accordingly, the insertion holes need to be formed in both the overlapped ear portions and each insertion hole needs to be formed to have a certain size. Furthermore, the width of the ear portion needs to be determined in accordance with the size of the insertion hole. Although the width of the outside ear portion should preferably be made less than that of the inside ear portion, the reduction in width of the outside ear portion is limited. In the prior art, it is difficult to further reduce the width of the ear portion and to make the location of the structure of the pivotal connection closer to the inner surface of the cavity in the bendable tube.
In the conventional structure, unless a certain thickness is maintained for both the ear portions for pivotally connecting the adjacent joint rings, coupling strength cannot be ensured. This, too, is a factor which prevents the location of the structure of the pivotal connection section from being made closer to the inner surface of the cavity in the bendable tube.
Moreover, in the conventional structure, since the rivet-like shaft pin for connecting both the overlapped ear portions is fixed by caulking, the strength of retention of the shaft pin is relatively low. In order to ensure strength for preventing removal, there is a need to increase the diameter of the insertion hole for pivotal connection and the diameter of the shaft pin. Consequently, it is required to increase the width of the ear portion and the diameter of the shaft pin. Accordingly, the entire pivotal connection section becomes larger and this prevents the location of the structure of the pivotal connection section from being made closer to the inner surface of the cavity in the bendable tube.
Besides, since the shaft pin is of the rivet type and requires fixation by caulking, the assembling process therefor is time-consuming.
The above problems are common to all endoscopes. In the case of an endoscope with a small-diameter insertion section, however, the width and thickness of the ear portion are smaller and these problems become more serious.